Our long term goal is to understand the cellular physiology of vertebrate photoreceptors. The research during this grant period focuses on membrane and intracellular events involved in the generation of the rod light response. The specific aims are: 1) to use patch clamp recording techniques to study the properties of the light-sensitive channels in the outer segment surface membrane. The emphasis of this work will be to investigate how the channels are influenced by external Ca, light and voltage. 2) To use the same recording technique to document the changes in the properties of outer segment membrane as it ages and undergoes modifications associated with the shedding process. 3) To study the influence of sulfhydral reagents on the ionic currents in excised patches of outer segment membrane. Particular attention will be placed on understanding the basis of the single channel currents evoked by dithiothreitol and their relationship to other outer segment ion channels. 4) To understand the control conditions necessary for stable long term recording from rods during internal dialysis. The motivation is to find a method to study the internal pharmacology of the transduction process. 5) To produce in vivo alterations in rod disks through intraoccular injection of compounds. The goal of these experiments is to study the intradiskal events evoked by light. 6) To use the above technique in conjunction with metallochromic Ca indicators to measure the light-evoked changes in intradiskal Ca. The outlined research will provide fundamental information about the physiology of rods in general and about the properties of outer segment surface membrane in particular. This will further our basic understanding of photoreception and enlarge our view of receptor biology. The latter is crucial for a full understanding of the pathophysiology of blindness caused by degenerative retinal diseases such as retinitis pigmentosa.